1. Field
This application relates generally to wireless communication and more specifically, but not exclusively, to communication employing multiple duty cycle levels.
2. Introduction
Wireless communication systems may be designed to support various end uses. To support such uses, one or more tradeoffs may be made in the implementation of a given system in terms of power consumption, latency, channel interference, channel usage, and other system parameters. For example, some networks may be used to provide connectivity for battery operated devices (e.g., a device that is relatively small and/or portable).
In some aspects, it is desirable to reduce the power consumption of such devices. For example, a device that consumes less power may utilize a smaller battery. Consequently, the device may potentially be manufactured in a smaller form factor and at a lower cost. In addition, a device that consumes less power may require less frequent battery recharges or battery replacements. In this case, the device may be more convenient for a user to use and may provide a lower overall cost of ownership.
Some types of networks (e.g., IEEE 802.15.1 and 802.15.4) may support power-down strategies that enable a device to reduce its overall power consumption. Here, if a device is no longer transmitting or receiving packets, the device may power down certain portions of the device (e.g., the radio) for a period of time.
In some cases, a receiving device may awake from a low power state at regular scan intervals to determine whether a transmitting device is attempting to transmit data. The receiving device may scan for a defined scan time that shorter than the duration of the scan interval. The ratio of the scan time over the scan interval may be referred to as the duty cycle of the low power state.
The transmitting device may remain in its low power state until it has a packet to send. When there is a packet to send, the transmitting device pages the receiving device to initiate transmission of the packet. Here, the transmitting device may repeatedly transmit a paging message to ensure that the receiving device receives the paging message during one of the receiving device's low power scans.
Upon receipt of a paging message, the receiving device may send a response to the transmitting node whereby both devices move to an active state. During the active state the receiving device continuously scans for incoming packets (i.e., the duty cycle is 100%). If there are no packet exchanges for a defined period of time (e.g., a timeout period), the transmitting and receiving nodes return to the low power state.
In some aspects, the duration of the timeout period is a tradeoff between latency and duty cycling. If the timeout period is long, the receiving device may waste power scanning for packets. For example, a relatively large amount of power may be wasted when supporting low data rate applications or when there are a relatively large number of paging false alarms. On the other hand, if the timeout period is short, the longer low power scan interval tends to dominate the latency. Moreover, a short timeout period may not effectively accommodate exponential back-offs associated with congestion control.